E f -Current Contributes to Whole-Cell Calcium Current in Low Calcium in Frog Sympathetic Neurons

• Published in: Journal of neurophysiology 2001-09, Vol.86 (3), p.1156-1163
• Main Authors: Liang, Haoya, Elmslie, Keith S.
• Format: Article
• Language: English
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.2001.86.3.1156

Because Ca 2+ plays diverse roles in intracellular signaling in neurons, several types of calcium channels are employed to control Ca 2+ influx in these cells. Our experiments focus on resolving the paradox of why whole-cell current has not been observed under typical recording conditions for one type of calcium channel that is highly expressed in frog sympathetic neurons. These channels, referred to as E f -channels, are present in the membrane at a density greater than the channels that carry ∼90% of whole-cell current in low Ba 2+ ; but, E f -current has not been detected in low Ba 2+ . Using Ca 2+ instead of Ba 2+ as the charge carrier, we recorded a possible E-type current in frog sympathetic neurons. The current was resistant to specific blockers of N-, L-, and P/Q-type calcium channels but was more sensitive to Ni 2+ block than was N- or L-current. Current amplitude in Ca 2+ is slightly greater than that in Ba 2+ . In 3 mM Ca 2+ , the current contributed ∼12% of total current at peak voltage and increased at voltages more hyperpolarized to the peak, reaching ∼40% at −30 mV, where whole-cell current starts to activate. The presence of E f -current in 3 mM Ca 2+ suggests a potential role for E f -channels in regulating calcium influx into sympathetic neurons.